Lapatinib (N-[3-chloro-4-[(3-fluorophenyl)methyoxy]phenyl]-6-[5-[2-methylsulfonylethyl-amino)methyl]-2-furyl] quinazolin-4-amine) is used in the form of lapatinib ditosylate as an oral drug to treat breast cancer and other solid tumors. It reversibly blocks phosphorylation of the epidermal growth factor receptor (EGFR), ErbB2, Erk-1 Erk-2 kinases, and AKT kinases. It also inhibits cyclin D protein levels in tumor cell lines and xenografts. It acts as a dual tyrosine kinase inhibitor that interrupts the HER2/neu and EGFR pathways, resulting in a decrease in tumor-causing cancer stem cells. It is typically used in combination therapy (e.g., with capecitabine) to treat patients with certain types of advanced breast cancer. Although it is apparently fairly well tolerated by patients, with the most common side effects being diarrhea, fatigue, nausea, and rashes, it has been associated with liver damage that can be severe or life-threatening. QT-prolongation has also been reported. Lapatinib is used with caution in patients with hypokalemia, hypomagnesmia, congenital long QT syndrome, or with co-administration of medications known to cause QT-prolongation. There have been reports of reversible decreased left ventricular function when used in combination with capecitabine (See, NCI Cancer Drug Information, FDA Approval for Lapatinib Ditosylate [Tykerb®]). Thus, there is a need for similarly or more effective drugs with an improved safety profile.